byobu-select-backend: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/byobu-select-backend - from package: byobu

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/byobu-select-backend - from package: byobu

You may install the required package with command apt-get install {package}

Error in other languages:
byobu-select-backend: bevel nie gevind nie
byobu-select-backend: comandă negăsită
byobu-select-backend: comando não encontrado
byobu-select-backend: commande introuvable
byobu-select-backend: command not found
byobu-select-backend: käsku ei ole
byobu-select-backend: không tìm thấy lệnh
byobu-select-backend: komanda nerasta
byobu-select-backend: Kommando nicht gefunden.
byobu-select-backend: kommandot finns inte
byobu-select-backend: komut yok
byobu-select-backend: nie znaleziono polecenia
byobu-select-backend: níor aimsíodh an t-ordú
byobu-select-backend: no se encontró la orden
byobu-select-backend: no s'ha trobat l'ordre
byobu-select-backend: opdracht niet gevonden
byobu-select-backend: parancs nem található
byobu-select-backend: perintah tidak ditemukan
byobu-select-backend: príkaz nenájdený
byobu-select-backend: příkaz nenalezen
byobu-select-backend: команда не найдена
byobu-select-backend: командата не е открита
byobu-select-backend: 命令找不到
byobu-select-backend: コマンドが見つかりません